The present invention relates to improvements in methods and mechanism of forming material which is used for making multiple bags. More particularly, the invention relates to a method and mechanism for arranging and handling the film and the strip for the fasteners for the bags and for joining the fastener strips to the film by high speed continuous heat sealing means such as by an ultrasonic sealing process in an improved manner which forms an improved bag and which is capable of continous fast production operation, that can be used in conjunction with extrusion operations.
In the formation of plastic film bags of the type referred to, the bags are of plastic film and usually formed with a folded bottom edge and with side edges sealed to each other. Flexible reclosable plastic fastener strips are sealed to the top edges of the bags thereby providing a reclosable sealable bag unit.
The fastener strips may take various forms such as shown in U.S. Pat. No. 2,780,261, Svec et al.
In the manufacture of bags such as illustrated in the above Svec et al. Patent, the bag bodies are formed of a thin lightweight plastic film which is extruded separately from the fastener. The fastener strips are extruded of a material and with a process that provides interlocking rib and groove elements carefully shaped and sized so that they will interlock when pressed together and will separate when pulled apart by opening flanges. These strips have web portions which are sealed to the film of the bag. It has been discovered that the bags in question can be manufactured by a multiple operation, that is, the material for making the bags can be formed so that two bag bodies project from a center assembly of the fastener strips. By cross cutting and scanning across the length of the material made, two bags are formed simultaneously. Since the overall cost of the completed bags is a function of the speed at which they can be manufactured, it is important that the length of material from which the bags are to be made can be made smoothly and rapidly at production rates of speeds, and in a reliable fashion. Improper joining of the fastener strips to the film of the bag will result in leaks in the bag, and in bags that will not properly close or cannot be reopened due to distortion of the fasteners because of misalignment. Also the amount of heat for joining the fastener to the bag wall will have an effect on the seal. If insufficient heat is applied, the seal will be inadequately formed so that the bag will leak, or the fastener web will peel away from the film to which it is attached. If too much heat is applied, the plastic will melt away so that there may be holes in the wall of the bag as mentioned above. It is also important for the fastener strips and the bag film to be accurately oriented with respect to each other. If the film is not properly positioned relative to the web portion of the fastener strips, a good seal may not result, and projecting raw edges of plastic on the inside of the bag can form crevices in which the contents of the bag will be caught, or if on the outside of the bag, said edges will tend to be torn apart by the user of the bag who will mistake these edges for the fastener opening lips. In the described form of manufacture, the fastener and the film are made separately by an extrusion process and then joined together shortly thereafter in an in-line process featuring continuous heat sealing of the strip to the film. Heretofore, fastener bags were made in an operation which required, in addition to the cross seal, attaching the fastener to the film during the bag making operation by intermittent overlapping sealing of the fastener web to the film, which in turn, cut down on the speed of the operation and reliability of the fastener seal. This was because each seal cycle first required a build up of heat and then a cooling of the seal formed before the operation could be repeated. This prevented the fastener and the film from being attached together continuously as they were being extruded.
Additionally, the heat could never be closely controlled since it was, as indicated, continously varying through its cycle. Under the present invention, once the optimum extrusion speeds have been reached, the heating means required for joining the fastener to the film can be set and maintained within a fairly accurate degree. The system described also has an advantage over methods of making a film and fastener integrally in that it allows the use of the most desirable resins for the film, where clarity and strength are required, and for the fastener where sufficient slip and contour forming are required. Generally, the characteristics of the resins required for the fastener are not the same as those required for the film and integral fastener film constructions usually result in a compromise. Furthermore, by extruding the fastener and the film separately, the most desirable extrusion process and cooling and control can be used for each one, thereby increasing the speeds at which each can be manufactured over that at which they can be manufactured integrally.
Accordingly, one of the best ways of making reclosable fastener bags is to be able to join the fastener and the film together as they are being separately extruded, on a continuous reliable basis, and later converting the fastener film into the bags themselves. After joining of the strip to the film, the material is placed on a roll for shipment to a converter, who in turn, forms bags by cross cutting and sealing. It is essential to the original manufacturer of the material that it be properly made so that the material can be rolled and stored.
It is accordingly an object of the present invention to provide an improved mechanism for forming continuous material for making fastener bags which is capable of operating at extrusion production speeds and producing bag material which is accurately and reliably made.
Another object of the present invention is to provide a mechanism for continuously forming material for making multiple bags, which can operate at extrusion production speeds eliminating the possibility of forming melted holes in the plastic and insuring positive and optimum attachment between the bag film and fastener strips.
Still another object of the invention is to provide a mechanism which will utilize tubular film or folded sheet film or flat sheet film and will attach front and rear fastener strips for bags by simultaneous continuous production operation.
Other objects, advantages and features, and equivalent structures within the scope of the invention will become more apparent to those skilled in the art in connection with the teaching of the principles thereof in the specification, claims, and drawings in which: